Many functions of modern devices in automotive, consumer and industrial applications, such as converting electrical energy and driving an electric motor or an electric machine, rely on power semiconductor devices. For example, Insulated Gate Bipolar Transistors (IGBTs), Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) and diodes, to name a few, have been used for various applications including, but not limited to switches in power supplies and power converters.
For example, such power converter is a flyback converter, which typically employs a MOSFET as a switching element.
A flyback converter converts an input voltage into an output voltage and provides a galvanic isolation between these voltages by means of a transformer.
Known flyback converters can be divided into types based on the applied operation principle. A first type is based on a continuous conduction mode (CCM), wherein a primary winding of the transformer has a residual energy when the switching element is turned off. A second type is based on a Discontinuous Conduction Mode (DCM), wherein the primary winding has substantially no energy when the switching element is turned off.
The DCM type flyback converters can further be divided into two subgroups, namely fixed frequency DCM flyback converters and into variable frequency DCM flyback converters, the latter being also known as valley switching or Quasi Resonant (QR) flyback converters.
A QR flyback converter is a DCM flyback converter having a valley switching turn on. It is, e.g., used in low power switched-mode power supply applications such as in a charger, an adapter or an auxiliary supply.